bims-nenemi Biomed News
on Neuroinflammation, neurodegeneration and mitochondria
Issue of 2025–02–16
seventeen papers selected by
Marco Tigano, Thomas Jefferson University
  1. Pharmacologic activation of integrated stress response kinases inhibits pathologic mitochondrial fragmentation.
  2. Mitochondria-targeting siRNA screening identifies mitochondrial calcium uniporter as a factor involved in nucleoid morphology.
  3. TEFM facilitates transition from RNA synthesis to DNA synthesis at H-strand replication origin of mtDNA.
  4. Mitochondrial DNA removal is essential for sperm development and activity.
  5. Disruption of mitochondrial homeostasis and permeability transition pore opening in OPA1 iPSC-derived retinal ganglion cells.
  6. Mitochondrial Amount Determines Doxorubicin-Induced Cardiotoxicity in Cardiomyocytes.
  7. A microscopy-based screen identifies cellular kinases modulating mitochondrial translation.
  8. Mitofusin 2 displays fusion-independent roles in proteostasis surveillance.
  9. STING directly interacts with PAR to promote apoptosis upon acute ionizing radiation-mediated DNA damage.
  10. MOMP: A critical event in cell death regulation and anticancer treatment.
  11. CerS6 links ceramide metabolism to innate immune responses in diabetic kidney disease.
  12. Early Synapse-Specific Alterations of Photoreceptor Mitochondria in the EAE Mouse Model of Multiple Sclerosis.
  13. ArfGAP2 promotes STING proton channel activity, cytokine transit, and autoinflammation.
  14. Poldip2 promotes mtDNA elimination during Drosophila spermatogenesis to ensure maternal inheritance.
  15. Etoposide-induced cancer cell death: roles of mitochondrial VDAC1 and calpain, and resistance mechanisms.
  16. Secretory mitophagy: an extracellular vesicle-mediated adaptive mechanism for cancer cell survival under oxidative stress.
  17. Hexokinase-I directly binds to a charged membrane-buried glutamate of mitochondrial VDAC1 and VDAC2.
  1. Elife. 2025 Feb 12. pii: RP100541. [Epub ahead of print]13
    Pharmacologic activation of integrated stress response kinases inhibits pathologic mitochondrial fragmentation.
    Kelsey R Baron, Samantha Oviedo, Sophia Krasny, Mashiat Zaman, Rama Aldakhlallah, Prerona Bora, Prakhyat Mathur, Gerald Pfeffer, Michael J Bollong, Timothy E Shutt, Danielle A Grotjahn, R Luke Wiseman.
      Excessive mitochondrial fragmentation is associated with the pathologic mitochondrial dysfunction implicated in the pathogenesis of etiologically diverse diseases, including many neurodegenerative disorders. The integrated stress response (ISR) - comprising the four eIF2α kinases PERK, GCN2, PKR, and HRI - is a prominent stress-responsive signaling pathway that regulates mitochondrial morphology and function in response to diverse types of pathologic insult. This suggests that pharmacologic activation of the ISR represents a potential strategy to mitigate pathologic mitochondrial fragmentation associated with human disease. Here, we show that pharmacologic activation of the ISR kinases HRI or GCN2 promotes adaptive mitochondrial elongation and prevents mitochondrial fragmentation induced by the calcium ionophore ionomycin. Further, we show that pharmacologic activation of the ISR reduces mitochondrial fragmentation and restores basal mitochondrial morphology in patient fibroblasts expressing the pathogenic D414V variant of the pro-fusion mitochondrial GTPase MFN2 associated with neurological dysfunctions, including ataxia, optic atrophy, and sensorineural hearing loss. These results identify pharmacologic activation of ISR kinases as a potential strategy to prevent pathologic mitochondrial fragmentation induced by disease-relevant chemical and genetic insults, further motivating the pursuit of highly selective ISR kinase-activating compounds as a therapeutic strategy to mitigate mitochondrial dysfunction implicated in diverse human diseases.
    Keywords:  cell biology; human; integrated stress response; mitochondrial fragmentation; mitochondrial morphology; mouse; stress signaling
    DOI:  https://doi.org/10.7554/eLife.100541
  2. J Biochem. 2025 Feb 10. pii: mvaf008. [Epub ahead of print]
    Mitochondria-targeting siRNA screening identifies mitochondrial calcium uniporter as a factor involved in nucleoid morphology.
    Hirotaka Kanon, Takaya Ishihara, Reiko Ban-Ishihara, Azusa Ota, Tatsuki Yasuda, Aoi Ichikawa, Ruo Ueyama, Taiki Baba, Kohsuke Takeda, Emi Ogasawara, Naotada Ishihara.
      Mitochondria are believed to have originated from the endosymbiosis of bacteria and they still contain their own genome, which is called mitochondrial DNA (mtDNA). Under fluorescence microscopy of cultured mammalian cells, mtDNA is observed as numerous tiny dot-like structures called mitochondrial nucleoids. In live-imaging, the morphology and distribution of nucleoids are change dynamically, but the molecular details remain poorly understood. In this study, we constructed a custom siRNA library targeting 1,164 human mitochondria-related genes, and from live-imaging-based screening of HeLa cells, we identified that mitochondria calcium uniporter (MCU), a pore-forming subunit of the mitochondrial Ca2+ channel, is involved in nucleoid morphology. We found that suppression of MCU by RNAi induced the formation of highly enlarged nucleoids as well as respiratory dysfunction and that the re-introduction of MCU or treatment with Ca2+ ionophore recovered the enlarged nucleoid morphology. These results suggest that mitochondrial Ca2+ uptake via MCU is associated with nucleoid morphology. The constructed siRNA library might be widely applied to analyze the roles of mitochondrial proteins in various cellular events, making it useful to understand the multifaceted functions of mitochondria in human cells.
    Keywords:  Mitochondria; mitochondrial calcium ion; mitochondrial calcium uniporter; mitochondrial nucleoid; siRNA screening
    DOI:  https://doi.org/10.1093/jb/mvaf008
  3. Commun Biol. 2025 Feb 08. 8(1): 202
    TEFM facilitates transition from RNA synthesis to DNA synthesis at H-strand replication origin of mtDNA.
    Shigeru Matsuda, Masunari Nakayama, Yura Do, Takashi Ishiuchi, Mikako Yagi, Sjoerd Wanrooij, Kazuto Nakada, Fan-Yan Wei, Kenji Ichiyanagi, Hiroyuki Sasaki, Dongchon Kang, Takehiro Yasukawa.
      Transcription of human mitochondrial DNA (mtDNA) begins from specific transcription promoters. In strand-asynchronous mtDNA replication, transcripts from the light-strand promoter serve as primers for leading-strand synthesis at the origin of the H-strand replication (OH). A 7S DNA strand, a presumed aborted replication product, is also synthesized from OH. Transition from RNA synthesis to DNA synthesis at OH is crucial for balancing replication with transcription, yet the mechanism remains unclear. Herein, we examine the role of mitochondrial transcription elongation factor (TEFM) in this process. TEFM knockout results in decreased 7S DNA, strand-asynchronous replication intermediates, and mtDNA copy number, all of which are concordant with downregulation of RNA-to-DNA transition at OH. Conversely, levels of tRNAs encoded near transcription promoters increase, indicating enhanced transcription initiation frequency. Taken together, we propose that, in addition to conferring processivity to the mitochondrial RNA polymerase, TEFM plays a crucial role in maintaining the balance between mitochondrial transcription and replication.
    DOI:  https://doi.org/10.1038/s42003-025-07645-4
  4. EMBO J. 2025 Feb 11.
    Mitochondrial DNA removal is essential for sperm development and activity.
    Zhe Chen, Fan Zhang, Annie Lee, Michaela Yamine, Zong-Heng Wang, Guofeng Zhang, Christian Combs, Hong Xu.
      Active mitochondrial DNA (mtDNA) elimination during spermatogenesis has emerged as a conserved mechanism ensuring the uniparental mitochondrial inheritance in animals. However, given the existence of post-fertilization processes degrading sperm mitochondria, the physiological significance of mtDNA removal during spermatogenesis is not clear. Here we show that mtDNA clearance is indispensable for sperm development and activity. We uncover a previously unappreciated role of Poldip2 as a mitochondrial exonuclease that is specifically expressed in late spermatogenesis and required for sperm mtDNA elimination in Drosophila. Loss of Poldip2 impairs mtDNA clearance in elongated spermatids and impedes the progression of individualization complexes that strip away cytoplasmic materials and organelles. Over time, poldip2 mutant sperm exhibit marked nuclear genome fragmentation, and the flies become completely sterile. Notably, these phenotypes were rescued by expressing a mitochondrially targeted bacterial exonuclease, which ectopically removes mtDNA. Our work illustrates the developmental necessity of mtDNA clearance for effective cytoplasm removal at the end of spermatid morphogenesis, and for preventing potential nuclear-mitochondrial genome imbalance in mature sperm, in which nuclear genome activity is shut down.
    Keywords:   Drosophila spermatogenesis; EndoG; Exonuclease; Male Sterile; Maternal Inheritance
    DOI:  https://doi.org/10.1038/s44318-025-00377-5
  5. Acta Neuropathol Commun. 2025 Feb 13. 13(1): 28
    Disruption of mitochondrial homeostasis and permeability transition pore opening in OPA1 iPSC-derived retinal ganglion cells.
    Michael Whitehead, Joshua P Harvey, Paul E Sladen, Giada Becchi, Kritarth Singh, Yujiao Jennifer Sun, Thomas Burgoyne, Michael R Duchen, Patrick Yu-Wai-Man, Michael E Cheetham.
      Dominant optic atrophy (DOA) is the most common inherited optic neuropathy, characterised by the selective loss of retinal ganglion cells (RGCs). Over 60% of DOA cases are caused by pathogenic variants in the OPA1 gene, which encodes a dynamin-related GTPase protein. OPA1 plays a key role in the maintenance of the mitochondrial network, mitochondrial DNA integrity and bioenergetic function. However, our current understanding of how OPA1 dysfunction contributes to vision loss in DOA patients has been limited by access to patient-derived RGCs. Here, we used induced pluripotent stem cell (iPSC)-RGCs to study how OPA1 dysfunction affects cellular homeostasis in human RGCs. iPSCs derived from a DOA+ patient with the OPA1 R445H variant and isogenic CRISPR-Cas9-corrected iPSCs were differentiated to iPSC-RGCs. Defects in mitochondrial networks and increased levels of reactive oxygen species were observed in iPSC-RGCs carrying OPA1 R445H. Ultrastructural analyses also revealed changes in mitochondrial shape and cristae structure, with decreased endoplasmic reticulum (ER): mitochondrial contact length in DOA iPSC-RGCs. Mitochondrial membrane potential was reduced and its maintenance was also impaired following inhibition of the F1Fo-ATP synthase with oligomycin, suggesting that mitochondrial membrane potential is maintained in DOA iPSC-RGCs through reversal of the ATP synthase and ATP hydrolysis. These impairments in mitochondrial structure and function were associated with defects in cytosolic calcium buffering following ER calcium release and store-operated calcium entry, and following stimulation with the excitatory neurotransmitter glutamate. In response to mitochondrial calcium overload, DOA iPSC-RGCs exhibited increased sensitivity to opening of the mitochondrial permeability transition pore. These data reveal novel aspects of DOA pathogenesis in R445H patient-derived RGCs. The findings suggest a mechanism in which primary defects in mitochondrial network dynamics disrupt core mitochondrial functions, including bioenergetics, calcium homeostasis, and opening of the permeability transition pore, which may contribute to vision loss in DOA patients.
    Keywords:  Calcium homeostasis; Dominant optic atrophy; Mitochondrial networks; Neurodegeneration; OPA1; Retinal ganglion cells; iPSCs
    DOI:  https://doi.org/10.1186/s40478-025-01942-z
  6. Adv Sci (Weinh). 2025 Feb 07. e2412017
    Mitochondrial Amount Determines Doxorubicin-Induced Cardiotoxicity in Cardiomyocytes.
    Weiyao Xiong, Bin Li, Jianan Pan, Dongjiu Li, Haihua Yuan, Xin Wan, Yanjie Zhang, Lijun Fu, Junfeng Zhang, Ming Lei, Alex Chia Yu Chang.
      Doxorubicin, an anthracycline commonly used for treating cancer patients, is known for its cardiotoxic side-effects. Although dose-dependent, but susceptibility remains variable among patients, and childhood-exposure-adult-onset remains challenging. Besides topoisomerase toxicity, Doxorubicin is also toxic to the mitochondria yet the underlying late onset mechanism remains elusive. Here, it is observed that the mitochondrial copy number in PBMCs of patients treated with anthracycline chemotherapy is negatively correlated with the change in plasma BNP levels after treatment. Isogenic hiPSC-CMs are generated with high, norm, and low mitochondrial copy numbers using mitochondrial transplantation and the YFP-Parkin system. Remarkably, lower mitochondria copy number translates to lower IC50, suggesting increased susceptibility. Mitochondria supplementation by intramyocardial injection prevents doxorubicin induced heart failure. Mechanistically, doxorubicin treatment leads to mPTP opening and mitochondrial DNA (mtDNA) leakage. This mtDNA leakage event activates the cGAS-STING pathway and drives inflammation and myocardial senescence. Cardiomyocyte-specific knockout of Sting (Myh6-Cre/Stingflox/flox; StingCKO) and over expression of mitochondrial tagged DNase1 in mice partially rescue doxorubicin-induced cardiac dysfunction. In conclusion, the work establishes a negative correlation between cardiomyocyte mitochondrial copy number and doxorubicin toxicity. Molecularly, it is demonstrated that mtDNA leakage activates cGAS-STING pathway and accelerates myocardial dysfunction. These insights offer new co-administration strategies for cancer patients.
    Keywords:  cGAS‐STING; doxorubicin induced cardiotoxicity; mitochondrial amount; mitochondrial transplantation; senescence
    DOI:  https://doi.org/10.1002/advs.202412017
  7. Cell Rep. 2025 Jan 28. pii: S2211-1247(24)01494-3. [Epub ahead of print]44(1): 115143
    A microscopy-based screen identifies cellular kinases modulating mitochondrial translation.
    Roya Yousefi, Luis Daniel Cruz-Zaragoza, Anusha Valpadashi, Carina Hansohn, Drishan Dahal, Ricarda Richter-Dennerlein, Silvio Rizzoli, Henning Urlaub, Peter Rehling, David Pacheu-Grau.
      Mitochondrial DNA encodes 13 subunits of the oxidative phosphorylation (OXPHOS) system, which are synthesized inside the organelle and essential for cellular energy supply. How mitochondrial gene expression is regulated and integrated into cellular physiology is little understood. Here, we perform a high-throughput screen combining fluorescent labeling of mitochondrial translation products with small interfering RNA (siRNA)-mediated knockdown to identify cellular kinases regulating translation. As proof of principle, the screen identifies known kinases that affect mitochondrial translation, and it also reveals several kinases not yet linked to this process. Among the latter, we focus on the primarily cytosolic kinase, fructosamine 3 kinase (FN3K), which localizes partially to the mitochondria to support translation. FN3K interacts with the mitochondrial ribosome and modulates its assembly, thereby affecting translation. Overall, our work provides a reliable approach to identify protein functions for mitochondrial gene expression in a high-throughput manner.
    Keywords:  CP: Metabolism; CP: Molecular biology; cellular kinases; click chemistry; mito-FUNCAT; mitochondrial translation; siRNA library
    DOI:  https://doi.org/10.1016/j.celrep.2024.115143
  8. Nat Commun. 2025 Feb 10. 16(1): 1501
    Mitofusin 2 displays fusion-independent roles in proteostasis surveillance.
    Mariana Joaquim, Selver Altin, Maria-Bianca Bulimaga, Tânia Simões, Hendrik Nolte, Verian Bader, Camilla Aurora Franchino, Solenn Plouzennec, Karolina Szczepanowska, Elena Marchesan, Kay Hofmann, Marcus Krüger, Elena Ziviani, Aleksandra Trifunovic, Arnaud Chevrollier, Konstanze F Winklhofer, Elisa Motori, Margarete Odenthal, Mafalda Escobar-Henriques.
      Mitochondria are essential organelles and their functional state dictates cellular proteostasis. However, little is known about the molecular gatekeepers involved, especially in absence of external stress. Here we identify a role of MFN2 in quality control independent of its function in organellar shape remodeling. MFN2 ablation alters the cellular proteome, marked for example by decreased levels of the import machinery and accumulation of the kinase PINK1. Moreover, MFN2 interacts with the proteasome and cytosolic chaperones, thereby preventing aggregation of newly translated proteins. Similarly to MFN2-KO cells, patient fibroblasts with MFN2-disease variants recapitulate excessive protein aggregation defects. Restoring MFN2 levels re-establishes proteostasis in MFN2-KO cells and rescues fusion defects of MFN1-KO cells. In contrast, MFN1 loss or mitochondrial shape alterations do not alter protein aggregation, consistent with a fusion-independent role of MFN2 in cellular homeostasis. In sum, our findings open new possibilities for therapeutic strategies by modulation of MFN2 levels.
    DOI:  https://doi.org/10.1038/s41467-025-56673-5
  9. Cell Death Differ. 2025 Feb 12.
    STING directly interacts with PAR to promote apoptosis upon acute ionizing radiation-mediated DNA damage.
    Yirong Sun, Saba R Aliyari, Kislay Parvatiyar, Lulan Wang, Anjie Zhen, Wei Sun, Xiaobo Han, Adele Zhang, Ethan Kato, Helen Shi, Elena De Schutter, William H McBride, Samuel W French, Genhong Cheng.
      Acute ionizing radiation (IR) causes severe DNA damage, leading to cell cycle arrest, cell death, and activation of the innate immune system. The role and signaling pathway of stimulator of interferon genes (STING) in IR-induced tissue damage and cell death are not well understood. This study revealed that STING is crucial for promoting apoptosis in response to DNA damage caused by acute IR both in vitro and in vivo. STING binds to poly (ADP‒ribose) (PAR) produced by activated poly (ADP‒ribose) polymerase-1 (PARP1) upon IR. Compared with that in WT cells, apoptosis was suppressed in Stinggt-/gt- cells. Excessive PAR production by PARP1 due to DNA damage enhances STING phosphorylation, and inhibiting PARP1 reduces cell apoptosis after IR. In vivo, IR-induced crypt cell death was significantly lower in Stinggt-/gt- mice or with low-dose PARP1 inhibitor, PJ34, resulting in substantial resistance to abdominal irradiation. STING deficiency or inhibition of PARP1 function can reduce the expression of the proapoptotic gene PUMA, decrease the localization of Bax on the mitochondrial membrane, and thus reduce cell apoptosis. Our findings highlight crucial roles for STING and PAR in the IR-mediated induction of apoptosis, which may have therapeutic implications for controlling radiation-induced apoptosis or acute radiation symptoms. STING responds to acute ionizing radiation-mediated DNA damage by directly binding to poly (ADP-ribose) (PAR) produced by activated poly (ADP-ribose) polymerase-1 (PARP1), and mainly induces cell apoptosis through Puma-Bax interaction. STING deficiency or reduced production of PAR protected mice against Acute Radiation Syndrome.
    DOI:  https://doi.org/10.1038/s41418-025-01457-z
  10. Biochim Biophys Acta Rev Cancer. 2025 Feb 11. pii: S0304-419X(25)00022-8. [Epub ahead of print] 189280
    MOMP: A critical event in cell death regulation and anticancer treatment.
    Dan Liu, Ziqi Liu, Yan Hu, Wei Xiong, Dan Wang, Zhaoyang Zeng.
      Mitochondrial outer membrane permeabilization (MOMP) refers to the increase in permeability of the mitochondrial outer membrane, allowing proteins, DNA, and other molecules to pass through the intermembrane space into the cytosol. As a crucial event in the induction of apoptosis, MOMP plays a significant role in regulating various forms of cell death, including apoptosis, ferroptosis, and pyroptosis. Importantly, MOMP is not a binary process of "all-or-nothing." Under sub-lethal stress stimuli, cells may experience a phenomenon referred to as minority MOMP (miMOMP), where only a subset of mitochondria undergo functional impairment, thereby disrupting the normal life cycle of the cell. This can lead to pathological and physiological changes such as tumor formation, cellular senescence, innate immune dysfunction, and chronic inflammation. This review focuses on the diversity of MOMP events to elucidate how varying degrees of MOMP under different stress conditions influence cell fate. Additionally, it summarizes the current research progress on novel antitumor therapeutic strategies targeting MOMP in clinical contexts.
    Keywords:  Anticancer treatment; BCL-2 family protein; MOMP; Minority MOMP; Mitochondria
    DOI:  https://doi.org/10.1016/j.bbcan.2025.189280
  11. Nat Commun. 2025 Feb 11. 16(1): 1528
    CerS6 links ceramide metabolism to innate immune responses in diabetic kidney disease.
    Zijing Zhu, Yun Cao, Yonghong Jian, Hongtu Hu, Qian Yang, Yiqun Hao, Houhui Jiang, Zilv Luo, Xueyan Yang, Weiwei Li, Jijia Hu, Hongyan Liu, Wei Liang, Guohua Ding, Zhaowei Chen.
      Ectopic lipid deposition, mitochondrial injury, and inflammatory responses contribute to the development of diabetic kidney disease (DKD); however, the mechanistic link between these processes remains unclear. In this study, we demonstrate that the ceramide synthase 6 (CerS6) is primarily localized in podocytes of the glomeruli and is upregulated in two different models of diabetic mice. Podocyte-specific CerS6 knockout ameliorates glomerular injury and inflammatory responses in male diabetic mice and in male mice with adriamycin-induced nephropathy. In contrast, podocyte-specific overexpression of CerS6 sufficiently induces proteinuria. Mechanistically, CerS6-derived ceramide (d18:1/16:0) can bind to the mitochondrial channel protein VDAC1 at Glu59 residue, initiating mitochondrial DNA (mtDNA) leakage, activating the cGAS-STING signaling pathway, and ultimately promoting an immune-inflammatory response in the kidney. Importantly, CERS6 expression is increased in podocytes from kidney biopsies of patients with DKD and focal segmental glomerulosclerosis (FSGS), and the expression level of CERS6 is correlated negatively with glomerular filtration rate and positively with proteinuria. Thus, our findings suggest that targeting CerS6 may be a potential therapeutic strategy for proteinuric kidney diseases.
    DOI:  https://doi.org/10.1038/s41467-025-56891-x
  12. Cells. 2025 Jan 30. pii: 206. [Epub ahead of print]14(3):
    Early Synapse-Specific Alterations of Photoreceptor Mitochondria in the EAE Mouse Model of Multiple Sclerosis.
    Dalia R Ibrahim, Karin Schwarz, Shweta Suiwal, Sofia Maragkou, Frank Schmitz.
      Multiple sclerosis (MS) is an inflammatory autoimmune disease of the central nervous system (CNS) linked to many neurological disabilities. The visual system is frequently impaired in MS. In previous studies, we observed early malfunctions of rod photoreceptor ribbon synapses in the EAE mouse model of MS that included alterations in synaptic vesicle cycling and disturbances of presynaptic Ca2+ homeostasis. Since these presynaptic events are highly energy-demanding, we analyzed whether synaptic mitochondria, which play a major role in synaptic energy metabolism, might be involved at that early stage. Rod photoreceptor presynaptic terminals contain a single large mitochondrion next to the synaptic ribbon. In the present study, we analyzed the expression of functionally relevant mitochondrial proteins (MIC60, ATP5B, COX1, PINK1, DRP1) by high-resolution qualitative and quantitative immunofluorescence microscopy, immunogold electron microscopy and quantitative Western blot experiments. We observed a decreased expression of many functionally relevant proteins in the synaptic mitochondria of EAE photoreceptors at an early stage, suggesting that early mitochondrial dysfunctions play an important role in the early synapse pathology. Interestingly, mitochondria in presynaptic photoreceptor terminals were strongly compromised in early EAE, whereas extra-synaptic mitochondria in photoreceptor inner segments remained unchanged, demonstrating a functional heterogeneity of photoreceptor mitochondria.
    Keywords:  DRP1; MIC60; experimental autoimmune encephalomyelitis (EAE); extra-synaptic mitochondria; mitochondria; multiple sclerosis; retina; ribbon synapse; synaptic mitochondria
    DOI:  https://doi.org/10.3390/cells14030206
  13. Cell. 2025 Feb 05. pii: S0092-8674(25)00096-0. [Epub ahead of print]
    ArfGAP2 promotes STING proton channel activity, cytokine transit, and autoinflammation.
    Subhajit Poddar, Samuel D Chauvin, Christopher H Archer, Wei Qian, Jean A Castillo-Badillo, Xin Yin, W Miguel Disbennett, Cathrine A Miner, Joe A Holley, Teresa V Naismith, W Alexander Stinson, Xiaochao Wei, Yue Ning, Jiayuan Fu, Trini A Ochoa, Nehalee Surve, Shivam A Zaver, Kimberly A Wodzanowski, Katherine R Balka, Rajan Venkatraman, Canyu Liu, Kelly Rome, Will Bailis, Yoko Shiba, Sara Cherry, Sunny Shin, Clay F Semenkovich, Dominic De Nardo, Sunnie Yoh, Elisha D O Roberson, Sumit K Chanda, David J Kast, Jonathan J Miner.
      Stimulator of interferon genes (STING) transmits signals downstream of the cytosolic DNA sensor cyclic guanosine monophosphate-AMP synthase (cGAS), leading to transcriptional upregulation of cytokines. However, components of the STING signaling pathway, such as IRF3 and IFNAR1, are not essential for autoinflammatory disease in STING gain-of-function (STING-associated vasculopathy with onset in infancy [SAVI]) mice. Recent discoveries revealed that STING also functions as a proton channel that deacidifies the Golgi apparatus. Because pH impacts Golgi enzyme activity, protein maturation, and trafficking, we hypothesized that STING proton channel activity influences multiple Golgi functions. Here, we show that STING-mediated proton efflux non-transcriptionally regulates Golgi trafficking of protein cargos. This process requires the Golgi-associated protein ArfGAP2, a cell-type-specific dual regulator of STING-mediated proton efflux and signaling. Deletion of ArfGAP2 in hematopoietic and endothelial cells markedly reduces STING-mediated cytokine and chemokine secretion, immune cell activation, and autoinflammatory pathology in SAVI mice. Thus, ArfGAP2 facilitates STING-mediated signaling and cytokine release in hematopoietic cells, significantly contributing to autoinflammatory disease pathogenesis.
    Keywords:  ArfGAP2; Golgi trafficking; SAVI; STING; antiviral immunity; autoinflammation; cGAS; chemokines; cytokines; interferon
    DOI:  https://doi.org/10.1016/j.cell.2025.01.027
  14. EMBO J. 2025 Feb 11.
    Poldip2 promotes mtDNA elimination during Drosophila spermatogenesis to ensure maternal inheritance.
    Ziming Wang, Tirawit Meerod, Nuria Cortes-Silva, Ason C-Y Chiang, Ziyan Nie, Ying Di, Peiqiang Mu, Ankit Verma, Adam James Reid, Hansong Ma.
      Maternal inheritance of mitochondrial DNA (mtDNA) is highly conserved in metazoans. While many species eliminate paternal mtDNA during late sperm development to foster maternal inheritance, the regulatory mechanisms governing this process remain elusive. Through a forward genetic screen in Drosophila, we identified 47 mutant lines exhibiting substantial retention of mtDNA in mature sperm. We mapped one line to poldip2, a gene predominantly expressed in the testis. Disruption of poldip2 led to substantial mtDNA retention in mature sperm and subsequent paternal transmission to progeny. Further investigation via imaging, biochemical analyses and ChIP assays revealed that Poldip2 is a mitochondrial matrix protein capable of binding mtDNA. Moreover, we showed that ClpX, the key component of a major mitochondrial protease, interacts with Poldip2 to co-regulate mtDNA elimination in Drosophila spermatids. This study sheds light on the mechanisms underlying mtDNA removal during spermatogenesis and underscores the pivotal role of this process in safeguarding maternal inheritance.
    Keywords:  ClpXP; Paternal Leakage; Paternal mtDNA Elimination; Poldip2; mtDNA Maternal Inheritance
    DOI:  https://doi.org/10.1038/s44318-025-00378-4
  15. Mol Oncol. 2025 Feb 07.
    Etoposide-induced cancer cell death: roles of mitochondrial VDAC1 and calpain, and resistance mechanisms.
    Aditya Karunanithi Nivedita, Varda Shoshan-Barmatz.
      Etoposide is an inhibitor of DNA topoisomerase II, an enzyme essential for DNA transcription, replication, and chromosome segregation. It is well accepted that etoposide triggers cell death due to DNA damage. Our results indicate that multiple molecular mechanisms contribute to etoposide-induced apoptosis, including the overexpression of the mitochondrial voltage-dependent anion channel 1 (VDAC1) and its oligomerization, forming a mega-channel that releases pro-apoptotic proteins, thereby activating apoptosis. Etoposide induces C-terminal truncation of VDAC1 (VDAC1-ΔC) via the proteolytic actions of calpain-1 and asparagine endopeptidase (AEP). A calpain-specific inhibitor effectively prevented etoposide-induced VDAC1-ΔC formation, apoptosis, and the nuclear translocation of apoptosis-inducing factor (AIF). Additionally, etoposide upregulates the expression levels of apoptosis regulators (p53, Bax, p21, AIF) and of the proteases calpain and AEP. Etoposide-induced apoptosis and VDAC1 truncation are cell-type dependent and associated with calpain levels and activity. Etoposide-induced VDAC1-ΔC formation and apoptosis are tightly linked: as both display similar patterns of concentration- and time-dependence, both are inhibited by calpain and AEP inhibitors, as well as the VDAC1 oligomerization inhibitor VBIT-4, and are dependent on intracellular Ca2+. These findings highlight the complexity of etoposide's actions in different cellular contexts, suggest possible mechanisms of resistance, offer potential biomarkers for guiding etoposide treatment in cancer patients, and propose targeting VDAC1 and calpain as promising therapeutic strategies in cancer therapy.
    Keywords:  VDAC1; apoptosis; calpain; etoposide; mitochondria; topoisomerase inhibitors
    DOI:  https://doi.org/10.1002/1878-0261.13807
  16. Front Cell Dev Biol. 2024 ;12 1490902
    Secretory mitophagy: an extracellular vesicle-mediated adaptive mechanism for cancer cell survival under oxidative stress.
    Purva V Gade, Angela Victoria Rojas Rivera, Layla Hasanzadah, Sofie Strompf, Thomas Raymond Philipson, Matthew Gadziala, Atharva Tyagi, Arnav Bandam, Rithvik Gabbireddy, Fatah Kashanchi, Amanda Haymond, Lance A Liotta, Marissa A Howard.
      Mitophagy is a critically important survival mechanism in which toxic, aged, or defective mitochondria are segregated into mitophagosomes, which shuttle the damaged mitochondrial segments to the lysosome and proteasome for destruction. Cancer cells rely on mitophagy under conditions of high oxidative stress or increased energy demand. Oxidative stress can generate a large volume of damaged mitochondria, overwhelming lysosomal removal. Accumulated damaged mitochondria are toxic and their proper removal is crucial for maintaining mitochondrial health. We propose a new cancer cell mechanism for survival that is activated when the demand for segregating and eliminating damaged mitochondria exceeds the capacity of the lysosome or proteasome. Specifically, we show that tumor cells subjected to oxidative stress by carbonyl cyanide-3-chlorophenylhdrazone (CCCP) eliminate damaged mitochondria segments by bypassing the lysosome to export them outside the cell via extracellular vesicles (EVs), a process termed "secretory mitophagy". PINK1, the initiator of mitophagy, remains associated with the damaged mitochondria that exported in EVs. Using several types of cancer cells, we show that tumor cells treated with CCCP can be induced to switch over to secretory mitophagy by treatment with Bafilomycin A1, which blocks the fusion of mitophagosomes with lysosomes. Under these conditions, an increased number of PINK1 + EVs are exported. This is associated with greater cell survival by a given CCCP dose, enhanced mitochondrial ATP production, and reduced mitochondrial oxidative damage (membrane depolarization). Our data supports the hypothesis that secretory mitophagy is a previously unexplored process by which cancer cells adapt to survive therapeutic or hypoxic stress. Ultimately, our findings may inform new prevention strategies targeting pre-malignant lesions and therapeutic approaches designed to sensitize tumor cells to oxidative stress-inducing therapies.
    Keywords:  PINK1; cancer progression; cell survival; extracellular vesicles; mitophagy; oxidative stress
    DOI:  https://doi.org/10.3389/fcell.2024.1490902
  17. Commun Biol. 2025 Feb 10. 8(1): 212
    Hexokinase-I directly binds to a charged membrane-buried glutamate of mitochondrial VDAC1 and VDAC2.
    Sebastian Bieker, Michael Timme, Nils Woge, Dina G Hassan, Chelsea M Brown, Siewert J Marrink, Manuel N Melo, Joost C M Holthuis.
      Binding of hexokinase HKI to mitochondrial voltage-dependent anion channels (VDACs) has far-reaching physiological implications. However, the structural basis of this interaction is unclear. Combining computer simulations with experiments in cells, we here show that complex assembly relies on intimate contacts between the N-terminal α-helix of HKI and a charged membrane-buried glutamate on the outer wall of VDAC1 and VDAC2. Protonation of this residue blocks complex formation in silico while acidification of the cytosol causes a reversable release of HKI from mitochondria. Membrane insertion of HKI occurs adjacent to the bilayer-facing glutamate where a pair of polar channel residues mediates a marked thinning of the cytosolic leaflet. Disrupting the membrane thinning capacity of VDAC1 dramatically impairs its ability to bind HKI in silico and in cells. Our data reveal key topological and mechanistic insights into HKI-VDAC complex assembly that may benefit the development of therapeutics to counter pathogenic imbalances in this process.
    DOI:  https://doi.org/10.1038/s42003-025-07551-9
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